1. Field of the Invention
The invention relates to a method for controlling a vehicular refrigerating cycle, said refrigerating cycle comprising a variable capacity compressor, a condenser for condensing a refrigerant, an expansion valve, an evaporator for evaporating adiabatically expanded refrigerant, a by-pass line detouring said condenser, and a line switching means for either supplying the refrigerant compressed by the compressor to the condenser in a cooling mode or into the by-pass line in a heating mode, and a vehicular refrigerating cycle of the kind as disclosed above.
High efficiency engines as gasoline-injection type engines or gasoline direct injection type engines do not develop high cooling water temperatures, compared with conventional combustion engines. Using the cooling water for heating purposes does not allow to sufficiently heat the vehicle compartment.
2. Description of the Related Art
U.S. Pat. No. 4,893,748 already proposes to use a refrigerating cycle in a vehicle not only for cooling purposes, but also for heating purposes. The refrigerating cycle contains a bypass line detouring the condenser and directing high-pressure refrigerant gas discharged from the compressor directly into an evaporator arranged inside the vehicle compartment so that heat exchange may take place in the evaporator for auxiliary heating purposes. However, if the refrigerating cycle is left at rest after an operation in the cooling mode, refrigerant tends to accumulate in the condenser. If then the refrigerating cycle is operated thereafter in the heating mode, only a small amount of refrigerant is circulated deteriorating the auxiliary heating effect.
This disadvantage calls for operating the refrigerating cycle prior to an operation in the auxiliary heating mode for a short time in the cooling mode (filling operation) to collect refrigerant stored in the condenser and to transfer it to the evaporator or an accumulator.
To convey refrigerant out of the condenser in this condition it would be necessary that the evaporator pressure was lower than the condenser pressure. However, when the refrigerating cycle contains a variable capacity compressor the capacity of which automatically decreases with a decrease of its suction pressure, the condenser pressure automatically drops to about 2 atm. (absolute atmospheric pressure) if the ambient atmospheric temperature has dropped, e.g. to about -10.degree. C. It is known from practice to use a solenoid-operated pressure regulating valve for controlling the capacity of the variable capacity compressor in a refrigerating cycle of this kind. However, even if the solenoid is supplied with a permanent maximum driving operation current of, e.g., 1 Ampere (falling within a range in which the coil of the solenoid is not burnt) the suction pressure does not decrease to more than to e.g. 2.3 atm.(absolute atmospheric pressure). Consequently, the evaporator pressure remains higher than the condenser pressure. Refrigerant stored in the condenser fails to flow out of the condenser. In case of an ambient temperature of -30.degree. C. the condenser pressure even drops to about 1 atm. (absolute atmospheric pressure) so that it is even more difficult to collect refrigerant stored in the condenser for the heating mode and to obtain a sufficient heating effect.
EP 780 254 A discloses to provide an ejector in a heating loop to additionally obtain refrigerant from the condenser for the auxiliary heating mode operation.
DE 19 746 773 discloses a refrigerating cycle with a variable capacity compressor and a method for controlling the compressor when operating the refrigerating cycle in the heating mode. According to said method the refrigerating cycle directly starts in its heating mode. Refrigerant is sucked out of the condenser via a separate by-pass line connecting the inlet of the condenser and the inlet of the compressor. Furthermore, the capacity control mechanism of the compressor is overruled in the heating mode at least in case of low ambient temperatures such that said compressor operated with high capacity. However, this is carried out to generally increase the refrigerant pressure.